The present invention relates generally to improvements in touch-pad to dial pulse conversion units, and more particularly pertains to new and improved touch-pad to dial pulse conversion units for installation within a subscriber unit wherein the conversion unit can receive the touch-pad input signals at an asynchronous rate, the entire conversion unit being powered from the current on the tip and ring lines.
In the field of touch-pad to dial pulse conversion, it has been the practice to employ separately housed and separately powered logic circuitry for performing the function of converting touch-pad input signal to dial pulses that are recognizable by a central office switching network. The bulkiness of these units and the necessity for using a separate power source, such as batteries to power the conversion circuits, have detracted from the attractiveness of such a device. Attempts have been made to design a conversion circuit that can be incorporated into the subscriber station and also be powered from the central office line current. These attempts, so far as is known, have resulted in considerably decreased performance of the subscriber unit. As a consequence, such attempts have reverted back to the use of a back-up power source, for example, a rechargeable nickle cadmium type battery.
Besides the function of converting touch-pad signals to central office recognizible pulse trains,, the present invention provides for toll restriction at the subscriber unit that can be preset and reset according to the restriction parameters desired. Prior art toll restriction units usually function somewhere in the tip and ring circuit between a central office and a subscriber unit. This requires the toll restrictor circuitry to be housed in a container separate from the subscriber unit, thereby creating access and mounting problems.